1,2-Propanediol is a known substance as an industrially useful compound. As a conventional process for producing the compound, it is reported that 1) 3-chloro-1,2-propanediol is converted into glycidol in a solution of potassium hydroxide-methanol and then glycidol is catalytically hydrogenated to give the object substance (M. Ochiai, Biochem. Z., 293 (1935)).
Known processes for producing optically active substances of 1, 2-propanediol are 2) reduction of natural ethyl lactate (J. Amer. Chem. Soc., 107, 5210 (1985)), 3) reduction of hydroxyacetone in the presence of a chiral catalyst (J. Amer. Chem. Soc., 110, 629 (1988)), 4) asymmetry reduction of hydroxyacetone with yeast (Japanese Laid-open Patent Publication No. 059592/1995), 5) resolution of racemate with enzyme (Japanese Laid-open Patent Publication No. 030790/1994), etc.
In the case of the above-mentioned conventional processes, however, since 1.2 equivalents of the base is used to the starting compound in the process 1), it leads to forming by-products such as polymers and 3-methoxy-1,2-propanediol. Since it is difficult to separate these by-products from the object substance, the yield of the object substance is low (72%). Actually, when the reaction 1) was carried out on a large scale, the yield was lower (47% (see Comparative Example 2 mentioned later)). The process 2) has disadvantages in that both of optically active substances of 1,2-propanediol cannot arbitrarily be obtained because the starting material is a natural optically active substance and in that it is necessary to use lithium aluminium hydride, which is difficult to handle in a practical use and expensive, as a reducing agent. In the process 3), the optical purity of the obtained object substance is low (92%ee), and it needs troublesome steps wherein the optical purity is improved by recrystallization after conversion into a derivative in order to obtain the object substance having high optical purity. In the processes 4) and 5), only one optically active substance is obtained.
In view of the above-mentioned various problems, the object of the present invention is to provide a process for obtaining 1,2-propanediol or the optically active substances thereof, both arc the object substance, in high yields and at a low cost, using a readily available compound as a starting material.